The present invention relates to an apparatus for post-treating exhaust gases of an internal combustion engine, having a reduction catalytic converter used to reduce NOx ingredients of the exhaust gases and having a device that generates a pressure difference in the exhaust gas, in particular but not exclusively for self-igniting internal combustion engines or Diesel engines with an exhaust gas turbocharger.
As limit values for emissions drop steadily, the most varied apparatuses for post-treating exhaust gases of internal combustion engines have been developed in recent years. To achieve a reduction of NOx ingredients in exhaust gases, reduction catalytic converters have been developed, particularly for Diesel engines; typically these are subdivided into SCR catalytic converters, which have urea metering systems, and storage catalytic converters. The so-called SCR catalytic converters are regenerated by means of a supply of urea and/or ammonia reducing agent, while the so-called storage catalytic converters are regenerated with hydrocarbons of the entrained engine fuel, in so-called rich exhaust gas phases.
These rich exhaust gas phases can indeed be demonstrated internally of the engine in the lower rpm and load range, but at higher rpm and higher torque, metered addition of reducing agents directly into the exhaust system is necessary, and preheating of the reducing agent may be necessary.
German Patent Disclosure DE-A 196 25 447, discloses a device for post-treating exhaust gases of an internal combustion engine in which exhaust gases are enriched with the fuel before reaching a reduction catalytic converter. This enrichment is done via an evaporator device, which thus introduces the liquid reducing agent in preheated and prepared form into the exhaust gas stream.
European Patent Disclosure EP-A 0 381 236, discloses a corresponding system is known, which to remove nitrogen oxides from exhaust gases from a Diesel engine meters in ammonia as a reducing agent. In this last system, a turbocharger is also provided, which lowers the pressure of the exhaust gas. The solution of urea and water is metered in by means of compressed air.
Finally, U.S. Pat. No. 5,067,320, discloses a system which serves to combust exhaust gas particles in a combustion chamber designed for this purpose. The combustion chamber is supplied via two exhaust gas lines, one of which is equipped with a fuel supply in order to furnish a combustible mixture to the combustion chamber, by means of which mixture the exhaust gas particles of the remaining exhaust gas stream can be combusted. This combustion of exhaust gas particles, however, is diametrically opposed to the goal of a catalytic converter, since this poorly controllable combustion of soot particles produces additional nitrogen oxides.